The LHC has just passed a major milestone, by cooling one eighth of the machine to 1.9 K. Given that the temperature of outer space is about 3 K (the temperature of the cosmic microwavve background radiation), that makes the LHC very very cool indeed. The cold sector is 3.3 km long, and has over 200 of the big 2-in-1 superconducting dipole magnets in it. These are the magnets that will keep the particles going in a circle 27 km in circumference. This cooling operation has taken several months, starting in January, with many successful checks and tests along the way.

How do you bend a relativistic proton in a supercoooled magnet without creating a honking great gamma ray that reheats said magnet after penetrating the chamber wall? Or are the beam currents sufficiently low that there isn’t much radiation produced?

Martin Arrowsmith

Hi,

I was wondering if any of the authors or readers of this site has read Dan Brown’s “Angels and Demons,” and has any thoughts on how Brown portrays particle physics, LHC, or antimatter. It is a work of fiction, but Brown likes to write in the beginning about how his stories are “factual,” and never makes it clear when he tips into the fiction.

Thanks,
-Martin

Martin Arrowsmith

I also have another question about the LHC. In the book it says to keep the particles going around in cirlces, the magnetic fields have to be turned and off in rapid succession. Do these fields have to be turned on/off just as the particles reach the proximity? If so, how did we get that accuracy?

Martin Arrowsmith

I’m sorry, one last question. For those who haven’t read the book, but would like to answer this question, please read on. It is sort of a spoiler, so please read if you don’t intend on reading the book.

Brown states that his fictional scientists can contain antimatter by “building a reverse polarity vacuum to pull the antimatter positrons out of the accelerator before they could decay, and to separatethe particles between matter and antimatter, you could apply a magnetic field where matter arced one direction and antimatter arced opposites. To contain the matter in a canister, a magnetic field would be applied to suspend the antimatter from touching any matter.”

Forgive my rapid comment posting, but this is the last one.

Martin Arrowsmith

My words bit me. I forgot to ask my question. It was simply, how much of that is true or realistic?

@LabLemming: the beam tubes are equipped with shields to protect the cold bore. Yes, there’s a risk for heating and thus quenching the supraconductor magnets, but the amount of heat deposited has been calculated and will be absorbed by the liquid helium. Moreover, superfluid helium is an excellent heat conductor.

Aaron F.

Errrr… you mean they’re cooling 200 big superconducting magnets just like the one that exploded during a quench test earlier this month? *eyebrows*

Edo

No, that one exploded over a pressure test. And it is not the same magnets: those ones have not been designed by the Fermilab ;P

Ellipsis

Lab Lemming — that is exactly why LHC will be accelerating protons, rather than electrons, to 7 TeV *. Bremsstrahlung power is proportional to m^(-6) (where m is the mass of the accelerated particle) — see for example chapter 14-15 of Jackson, _Classical Electrodynamics_. P = (mu_0*q^2*a^2*E^6)/(6pi*m^6*c^7). Thus protons emit 10^18 times less total bremsstrahlung power than electrons.

* as well as the fact that, for the identical reason, the power bill for a 14 TeV circular e-p collider would bankrupt the world — hence the pursuit of linear, rather than circular, colliders when higher (> 100 GeV) energies for electron and positron beams, rather than protons, are considered